1. Technical Field
The present invention relates to imaging biologic samples in general, and to focusing the image of biologic samples in particular.
2. Background Information
Automated microscopy systems that take multiple images over the surface of a biologic sample generally require the imaging system to be re-focused for each field imaged. Re-focusing is necessary because the required precision of focus for such systems, at useful magnifications, can be as little as one micron and it is virtually impossible to hold the mechanical tolerances of the sample holder to these dimensions. To completely image even a small biologic sample quiescently residing within an analysis chamber such as that disclosed in U.S. Pat. No. 6,723,290, entitled “Container for Holding Biologic Fluid for Analysis”, it is necessary to take over a hundred individual images, and to perform this operation in a reasonable time, it is necessary to re-focus each image field as rapidly as possible.
Conventional automatic focusing techniques typically use characteristics of the image itself to acquire the proper focus, or may use a device that is independent of the image capture device, such as an interferometer or the like to measure and maintain a set distance between the objective lens and the subject. In the first case, it is typically necessary to take several image capture cycles with the image capture device to calculate the best point of focus. This multiple image process is time consuming and therefore not desirable. In the second case, the independent device typically adds complication and considerable expense to the imaging system. The present invention, in contrast, provides an inexpensive means of ensuring rapid focusing that is consistently accurate, one that can be used in a variety of imaging system configurations, and one that relies only on the imaging system itself.